The colors of an image to be photographed are highly affected by the ambient light. A warm ambient light is considered more red and less blue compared to a cool ambient light. A warm ambient light may be an incandescent light, such as using a tungsten filament (about 3000K). Morning or afternoon sun produces less warm ambient light (about 3500K). A cooler ambient light is a fluorescent light (about 4500K). Overhead-sun daylight, cloudy daylight, and shady daylight produce progressively cooler light (5000-10000K). A standard xenon flash produces a cool light (about 5500K) that tends to dominate the ambient light.
High quality digital cameras are manually controllable to select the type of existing ambient light. As a result of the selection, a particular compensation algorithm is performed on the color pixels to compensate for the color bias created by the ambient light so that the picture colors are truer.
Some digital camera can automatically detect the type of ambient light by color balance and other techniques. As a result, the camera's processor applies the appropriate one of a number of color compensation algorithms to correct any color bias due to the detected ambient light.
When a standard xenon flash is used in a camera, the camera assumes that the flash dominates the ambient light, and the color compensation algorithm selected by the camera is sometimes that associated with the use of flash. In certain situations, however, the flash and ambient light both substantially contribute to the image's illumination.
LEDs are becoming increasingly popular for use as a flash for small cameras, including cell phone cameras. This is because the LEDs do not need a high voltage pulse, required for a xenon flash, and the LED and its driver are much smaller than the xenon bulb and its driver. An LED may also be continuously turned on when taking a video using a digital camera.
Flash LEDs used today are typically a standard blue LED die covered with a YAG phosphor, where the yellow-green light emitted by the YAG phosphor is combined with the blue LED light leaking through the phosphor layer to produce a white light. The light is considered a cool light, with a color temperature of around 7000K.
A problem with LED flashes is that the flash color temperature does not match the ambient color temperature. Therefore, the image is illuminated by the combination of two light sources of different characteristics. Since the various automatic color compensation algorithms stored in the camera are specifically tailored to particular types of ambient light or to the flash by itself, even the most appropriate color compensation algorithm selected will not accurately compensate for the two very different illuminating light sources.
What is needed in the field of digital camera flashes is a flash system that works well in conjunction with the camera's color compensations algorithms to produce a picture with truer colors.